1. Field of the Invention
The present invention relates to an infrared ray sensor and, more particularly, to an uncooled pyroelectric infrared ray sensor in which an infrared ray absorption layer of a focal plate is composed of a silicon oxide film, and the infrared ray absorption layer, support arms and posts are integrated in a single body, and a method of fabricating the same.
2. Discussion of Related Art
A focal plate of a pyroelectric infrared ray sensor is an element that converts an incident infrared energy into a thermal energy to transmit it to a pyroelectric thin film and detects the variation of charges generated in a pyroelectric material at the same time as an electrical signal. Typically, a focal plate of an infrared ray sensor includes several parts such as a part for converting an incident infrared ray into a thermal energy, a part of the functional material for exhibiting differences of the electrical characteristics in accordance with the amount of the thermal energy, and a part of the metallic wiring for detecting the electrical signals in accordance with the differences of the electrical characteristics.
If an infrared ray is incident to a pyroelectric infrared ray sensor, the corresponding energy is delivered to the focal plate to raise the temperature of a pyroelectric thin film, thus generating variations of residual surface charges, that is, the inherent characteristic of a pyroelectric material. The variation of the generated charges is detected through a metallic wiring as minute currents. At this point, the minute currents equal to or less than pico-amperes (˜pA) are detected so that noise ratio of the element becomes an important factor for detecting the signals. For this reason, it is preferable that the focal plate including the pyroelectric thin film, the main component of the infrared ray sensor, has a configuration three-dimensionally separated from a substrate in order to avoid thermal noises.
FIG. 1 is a perspective view illustrating a conventional configuration of a pyroelectric infrared ray sensor, disclosed in the U.S. Pat. No. 6,087,661 entitled ‘Thermal Isolation of Monolithic Thermal Detector’, by Robert A. Owen et al. Such a pyroelectric infrared ray sensor has a configuration three-dimensionally separated from a substrate in consideration of thermal noises.
Referring to FIG. 1, a thermal sensor 36 mainly includes a thermal assembly 44 and a signal flow path 46. The thermal assembly 44 comprises a thermal sensing element 50 for generating a signal in accordance with thermal energy and a pair of electrodes 52 and 54 for collecting the signal generated by the thermal sensing element 50. The signal flow path 46 transmits the signal collected by the electrodes 52 and 54 to the substrate 34, and includes a pair of support arms 56 and 58 extending from each of electrodes 52 and 54 and connected to the substrate 34. The support arms 56 and 58 are supported by the posts 64 disposed on the contact pads 70 on the substrate 34 and support the thermal assembly 44 to be separated from the substrate 34. The support arms 56 and 58 are formed with a thermal insulating material, which provides electrical conductivity to transmit the signal collected by the electrodes 52 and 54 to the substrate 34.
The pyroelectric infrared ray sensor shown in FIG. 1 comprises not an infrared ray absorption layer but upper and lower electrodes 52 and 54 composed of an oxide film, which is transparent in an infrared wavelength band. For this reason, a part of the incident infrared ray is absorbed in the pyroelectric thin film and then absorbed again after reflected by a metallic thin film (not shown) formed on the surface of the substrate 34. In such a configuration, the upper and lower electrodes 52 and 54 of the focal plate assembly of the infrared ray sensor should be supported by two separate support arms 56 and 58.
Such a configuration is advantageously sensitive to the variation of the amount of the incident infrared ray by decreasing the thermal mass of the focal plate. However, the electrodes made of the thin oxide films should support the focal plate assembly. Therefore, such a configuration is structurally unstable, so that the process yield decreases. In addition, the top portion of the substrate must disadvantageously have a metallic thin film which functions as a reflecting mirror for reflecting the incident infrared ray from the substrate.